An ion source is a device that causes gas molecules to be ionized and then accelerates and emits the ionized gas molecules and/or atoms in a beam (ion beam) toward a substrate. Such an ion beam may be used for various purposes, including but not limited to cleaning a substrate, activation, polishing, etching, and/or deposition of thin-film coatings/layer(s). Example ion sources are disclosed, for example, in U.S. Pat. Nos. 7,030,390; 6,988,463; 6,987,364; 6,815,690; 6,812,648; 6,359,388; and application Ser. No. 10/986,456, the disclosures of which are all hereby incorporated herein by reference.
FIGS. 1-2 illustrate a conventional cold-cathode type ion source. In particular, FIG. 1 is a side cross-sectional view of an ion beam source with an ion beam emitting slit defined in the cathode, and FIG. 2 is a corresponding sectional plan view along section line II-II of FIG. 1. FIG. 3 is a sectional plan view similar to FIG. 2, for purposes of illustrating that the FIG. 1 ion beam source may have an oval and/or racetrack-shaped ion beam emitting slit as opposed to a circular ion beam emitting slit. Any other suitable shape also may be used.
Referring to FIGS. 1-3, the ion source includes a hollow housing made of a magneto conductive material, which is used as a cathode 5. Cathode 5 includes cylindrical or oval side wall 7, a closed or partially closed bottom wall 9, and an approximately flat top wall 11 in which a circular or oval ion emitting slit and/or aperture (also sometimes referred to as a “discharge gap”) 15 is defined. The bottom wall 9 and side walls 7 of the cathode 5 are optional. The outer cathode is typically made of 1008 steel at a substantial cost. Ion emitting slit/aperture 15 includes an inner periphery as well as an outer periphery. Deposit and/or maintenance gas supply aperture or hole(s) 21 is/are formed in bottom wall 9. Flat top wall 11 functions as an accelerating electrode. A magnetic system including a cylindrical permanent magnet 23 with poles N and S of opposite polarity is placed inside the housing between bottom wall 9 and top wall 11. The N-pole faces flat top wall 11, while the S-pole faces bottom wall 9. The purpose of the magnetic system with a closed magnetic circuit formed by the magnet 23 and cathode 5 is to induce a substantially transverse magnetic field (MF) in an area proximate to ion emitting slit 15.
The ion source may be entirely or partially within conductive wall 50, and/or wall 50 may at least partially define the deposition chamber. In certain instances, wall 50 may entirely surround the source and substrate 45, while in other instances the wall 50 may only partially surround the ion source and/or substrate.
A circular or oval shaped conductive anode 25, electrically connected to the positive pole of electric power source 29, is arranged so as to at least partially surround magnet 23 and be approximately concentric therewith. Anode 25 may be fixed inside the housing by way of insulative ring 31 (e.g., of ceramic). Anode 25 defines a central opening therein in which magnet 23 is located. The negative pole of electric power source 29 may be grounded and connected to cathode 5, so that the cathode is negative with respect to the anode. Generally speaking, the anode 25 is generally biased positive by several thousand volts. Meanwhile, the cathode (the term “cathode” as used herein includes the inner and/or outer portions thereof) is generally held at ground potential although it need not be. This is the case during aspects of source operation, including during a mode in which the source is being cleaned.
The conventional ion beam source of FIGS. 1-3 is intended for the formation of a unilaterally directed approximately tubular ion beam, flowing in the direction toward substrate 45. Substrate 45 may or may not be biased in different instances. The ion beam emitted from the area of slit/aperture 15 is in the form of a circle in the FIG. 2 embodiment and in the form of an oval (e.g., race-track) in the FIG. 3 embodiment.
The ion source of FIGS. 1-3 operates as follows in a depositing mode when it is desired that the ion beam from the source deposit at least one layer on substrate 45. A vacuum chamber in which the substrate 45 and slit/aperture 15 are located is evacuated, and a depositing gas (e.g., a hydrocarbon gas such as acetylene, or the like) is fed into the interior of the source via aperture(s) 21 or in any other suitable manner. A maintenance gas (e.g., argon) may also be fed into the source in certain instances, along with the depositing gas. Power supply 29 is activated and an electric field is generated between anode 25 and cathode 5, which accelerates electrons to high energy. Anode 25 is positively biased by several thousand volts, and cathode 5 may be at ground potential as shown in FIG. 1. Electron collisions with the gas in, and/or proximate to, aperture/slit 15 leads to ionization and a plasma is generated. “Plasma” herein means a cloud of gas including ions of a material to be accelerated toward substrate 45. The plasma expands and fills (or at least partially fills) a region including slit/aperture 15. An electric field is produced in slit 15, oriented in the direction substantially perpendicular to the transverse magnetic field, which causes the ions to propagate toward substrate 45. Electrons in the ion acceleration space in and/or proximate to slit/aperture 15 are propelled by the known E×B drift in a closed loop path within the region of crossed electric and magnetic field lines proximate to slit/aperture 15. These circulating electrons contribute to ionization of the gas (the term “gas” as used herein means at least one gas), so that the zone of ionizing collisions extends beyond the electrical gap between the anode and cathode and includes the region proximate to slit/aperture 15 on one and/or both sides of the cathode 5. For purposes of example, consider the situation where a silane and/or acetylene (C2H2) depositing gas is/are utilized by the ion source of FIGS. 1-3 in a depositing mode. The silane and/or acetylene depositing gas passes through the gap between anode 25 and cathode 5.
Reference will be made below to various steels conforming to the corresponding standards of the American Iron and Steel Institute (AISI), as will be appreciated by one of ordinary skill in the art.
Unfortunately, the ion source of FIGS. 1-3 suffers several drawbacks. In conventional ion sources, the outer cathode is manufactured from a single piece of 1008 mild steel. Manufacturing the outer cathode from 1008 mild steel is a costly endeavor. One reason the cost of 1008 steel is high is because 1008 mild steel itself is not readily available. Costs also are high because of the machining requirements associated with producing the outer cathode from such steel. More particularly, the costs of forming the outer cathode are high because the outer cathode has a complex design. Thus, a large piece of 1008 mild steel is required, even though a significant portion of it is sacrificed while machining the steel, to achieve the complex design. Furthermore, 1008 steel generally is difficult to machine, thus requiring higher labor and/or machining costs.
Furthermore, the body of conventional ion sources typically are manufactured from a single piece of mild steel. Manufacturing costs are high. This is because the complexity of the design of the ion source body similarly requires a significant amount of machining, and a large amount of material is lost in the machining process because the ion source body is machined from a large, solid piece of steel.
Thus, it will be appreciated that there exists a need in the art for an ion source that overcomes one or more of the above problems and/or other disadvantages.
Certain example embodiments of this invention provide a cathode for use in an ion source, wherein at least part of the cathode is formed from annealed 1018 mild steel. The cathode made from such 1018 mild steel maybe an inner cathode and/or an outer cathode.
Certain other example embodiments of this invention provide an ion source capable of emitting an ion beam. Such example embodiments may comprise an anode, an inner cathode, and an outer cathode, with one of the anode, the inner cathode, and the outer cathode having a discharge gap defined therein. A power supply may be in electrical communication with the anode, the inner cathode, and/or the outer cathode. At least one magnet may be capable of generating a magnetic field proximate to the discharge gap. The inner cathode and/or the outer cathode may be formed from annealed 1018 mild steel.
According to certain other example embodiments of this invention, a segmented cathode for use with an ion source is provided. Such example embodiments may comprise, for the segmented cathode, a substantially rectangular top portion; a substantially rectangular bottom portion; a substantially U-shaped left-side portion; and, a substantially U-shaped right-side portion. Optionally, a first set of notches disposed at each end of the top portion and bottom portion may be configured to engage with a second set of notches disposed at each end of the left-side portion and right-side portion. In certain example non-limiting embodiments, each of the top, bottom, left-side, and right-side portions may be machined to eliminate at least some of the material thereof. In certain non-limiting example embodiments, the segmented cathode may further comprise at least one hole, with one or more such hole(s) being configured to receive a bolt or the like, and with each bolt or the like being provided to attach the segmented cathode to an outer housing of the ion source. The segmented cathode may be an outer cathode in certain example instances.
In certain example embodiments of this invention, there is provided an ion source comprising: an anode, an inner cathode and an outer cathode, a discharge gap defined between the inner and outer cathodes; a power supply in electrical communication with one or more of the anode, the inner cathode, and/or the outer cathode; at least one magnet capable of generating a magnetic field proximate to the discharge gap; and wherein the inner cathode and/or the outer cathode comprises annealed 1018 mild steel.
In other example embodiments of this invention, there is provided a an ion source comprising an anode, a cathode, a discharge gap defined proximate the anode and cathode; a power supply in electrical communication with the anode and/or cathode; at least one magnet capable of generating a magnetic field proximate the discharge gap; and wherein the anode and/or cathode comprises 1018 mild steel.
In still further example embodiments of this invention, there is provided a method of making an ion source, the method comprising: providing an anode, providing a plurality of pieces comprising steel for an outer cathode, and attaching the plurality of pieces comprising steel together to form the outer cathode; providing an inner cathode; assembling the anode, inner cathode and outer cathode in an ion source apparatus so as to form a discharge gap of the ion source defined between the inner and outer cathodes.
In yet other example embodiments of this invention, there is provided a method of making an ion source, the method comprising: providing an anode, providing a steel U-channel; processing the U-channel to form at least an outer cathode for the ion source; assembling the anode, an inner cathode and the outer cathode formed using the U-channel in an ion source apparatus so as to form a discharge gap of the ion source defined between the inner and outer cathodes.